Biomass gasification generates a gas mixture (syngas) that constitutes a rich source of carbon and energy for the production of second-generation renewable fuels such as biomethane. However, the produced syngas composition (H₂/CO/CO₂) cannot be converted to natural gas grade biomethane due to stoichiometric limitations, and a waste stream of CO₂ is released unexploited in the atmosphere. The present study introduces the concept of biomass gasification coupled to syngas biomethanation with in-situ exogenous H₂ supply for the complete sequestration of the syngas carbon, the valorization of renewable excess electricity from wind and solar power and the production of biomethane satisfying the criteria for injection in the natural gas grid. Syngas biomethanation was executed by mixed microbial consortia in a trickle bed reactor at 37 °C and 60 °C. The assessment of the effects of the net inlet gas composition was performed according to a hereby proposed syngas quality index (\(SQI\)), which is based on the syngas content in compounds able to act as carbon and electron donors and the stoichiometry of methane production. The SQI of the stoichiometrically ideal syngas composition is 4. Values below 4 correspond to a stoichiometric carbon-moles excess while values above 4 correspond to a stoichiometric electron-moles excess. It was demonstrated that switching the SQI of the supplied syngas from 1.44 to 3.67 increased the CH₄ content in the outlet of the reactor from 30 to 72%, accompanied by an at least 1.2-fold increase of the CH₄ productivity. A SQI of 4.78 (> 4) resulted in a significant deterioration of the quality of the produced biomethane due to a high content (52–54%) of unconverted H₂ and because of thermodynamic limitations on carboxydotrophic hydrogenogenesis in thermophilic conditions. Maximal carbon sequestration and production of natural gas grade biomethane was shown to be feasible at a SQI = 3.98 in thermophilic conditions.

Graphic Abstract

中文翻译：

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通过合成气生物甲烷化结合H 2供气进行碳固存，可清洁生产天然气级生物甲烷

生物质气化产生混合气体（合成气），构成了丰富的碳和能源，用于生产第二代可再生燃料，例如生物甲烷。然而，由于化学计量上的限制，所产生的合成气成分（H ₂ / CO / CO ₂）不能转化为天然气级生物甲烷，并且CO ₂的废气流未被利用而释放到大气中。本研究介绍了生物质气化与原位外源H _2的合成气生物甲烷化结合的概念完全封存合成气碳的供应，风能和太阳能的可再生多余电力的增值以及满足注入天然气网标准的生物甲烷的生产。合成气的生物甲烷化反应是在37°C和60°C的滴流床反应器中通过混合微生物联合体进行的。根据特此提出的合成气质量指数（\（SQI \）），这是基于能够充当碳和电子供体的化合物中合成气的含量以及甲烷产生的化学计量。化学计量上理想的合成气组成的SQI为4。低于4的值对应于化学计量的碳摩尔过量，而高于4的值对应于化学计量的电子摩尔过量。已经证明，将供应的合成气的SQI从1.44切换到3.67将反应器出口中的CH ₄含量从30％增加到72％，同时使CH ₄生产率提高至少1.2倍。SQI为4.78（> 4）会导致产生的生物甲烷的质量显着下降，这是由于未转化的H ₂含量较高（52–54％）并且由于在嗜热条件下对羧基营养养分氢生成的热力学限制。在高温条件下，SQI = 3.98时，最大程度的固碳和生产天然气级生物甲烷是可行的。

图形摘要